.content{
    width: 640px;
    height: 640px;
    margin: 50px auto;
    position: relative;
}
.btn{
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    background-color: rgba(0,0,0,0.3);
    z-index: 2;

}
.btn button{
    background:none;
    border: none;
    position: absolute;
    left: 50%;
    top: 50%;
    background-size: 100% 100%;
    outline: none;
    /* 去掉点击时的蓝框 */
    cursor: pointer;
    /* 变小手 */
}
.startBtn button{
    width: 200px;
    height: 80px;
    background-image:url(../images/startGame.png) ;
    margin-left: -100px;
    margin-top: -40px;
}
.pauseBtn{
    display: none;
}
.pauseBtn button{
    width: 70px;
    height: 70px;
    background-image: url(../images/start.png);
    margin-left: -35px;
    margin-top: -35px;
}
#snakeWrap{
    width: 600px;
    height: 600px;
    background: #225675;
    border: 20px solid #7dd9ff;
    position: relative;
}
#snakeWrap div{
    width: 20px;
    height: 20px;
}
.snakeHead{
    background-image: url(../images/snake.png);
    background-size: cover;
   
}

.snakeBody{
    background-color: #9ddbb1;
    border-radius: 50%;
}
.food{
   background-image: url(../images/food.png);
   background-size: cover;
}